<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="app">
        <p>{{foo}}</p>
        <button @click="bijclick">Change it</button>
    </div>
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.13/dist/vue.js"></script>
    <script>


        var vm = new Vue({
            el: "#app",
            data: {

                foo: 'bar'
            },
            methods: {

                bijclick() {
                    this.foo = "baz"
                }
            }
        })
        Object.freeze('#app')
    </script>
</body>

</html>